1. Description of the Prior Art
An excess pressure device is known from the German Letters Pat. No. 1,564,673 in which a ring-shaped valve element formed of an elastic synthetic material closes a valve opening and is initially biased against the walls of the valve. The necessary bias is achieved due to the fact that the valve element is pressed against the housing by means of a rivet which holds a washer in place against the element. The diameter of the washer is dimensioned in such a way that the edge of the valve lip can lift off the valve dome.
After pressure balance is achieved, the inside of the capacitor housing is again closed in a gas-tight manner by means of the elastic restoring force of the valve element. The difficulty of this construction is in the fact that the valve element rests against the inner wall of the valve dome only with the force corresponding to the elastic constant of the material being used.
An earlier proposal provides that the washer is constructed in such a way that one of several recesses are located at its edge. By means of this arrangement, the size of the washer can be chosen so that the valve element is pressed rigidly against the inner edge of the valve dome and that it can yield only at those points where the recesses are located.
Another such device is shown in German Gebrauchsmuster No. 1,893,990. This device is formed in two parts which are connected to each other in the manner of a snap button. The difficulties in mounting the known pressure valves are due to the fact that the valve has to be mounted rigidly prior to the finishing of the capacitor housing. There is also the additional danger in such an arrangement that the release of excess pressure also causes liquid to become visible at the outside of the capacitor.
2. Field of the Invention
The field of art to which this invention pertains is relief valves and, in particular, to relief valves for electrical capacitors which are formed of an elastic or resilient type material.